1. Field of the Invention:
This invention relates to a method of treating surfaces having pores or fissures. More specifically it relates to an improved method of locking finely deposited particles, such as polytetrafluoroethylene, into the pores or fissures in a surface. Still more specifically it is related to an improved method of compacting said deposited particles in said fissures and then depositing or locking an additional amount of the finely divided particles in said fissures.
2. Related Prior Art:
U.S. Pat. Nos. 3,279,936 and 3,502,493 disclose and cover the process of depositing finely divided particles into the fissures or pores of a surface while the surface is at a raised temperature so that the fissures are in an enlarged or expanded condition and the particles are at a temperature at least 150.degree. F, preferably at least 300.degree. F below the temperature of the heated surface. After the particles are deposited in the fissures the temperature of the surface and of the particles is permitted to come to equilibrium with the result that the particles are locked into the fissures by interference fit. These particles, particularly when they are polytetrafluoroethylene, impart desirable properties, such as reduced friction and antisticking properties, to the treated surface.
Metal surfaces so treated have been used for many purposes such as metal stamping, drawing and forming, plastic extrusion, fabrication and sealing, rubber molding, etc. While the useful life of the metal articles used for these purposes has been extended tremendously by the treatment described in the above patents, it is found that eventually the repeated pressure of materials under the high working pressures used for these purposes causes some compaction of the locked particles into the fissures so that there is some space in the fissures into which debris such as lubricants or the material being compressed may become lodged in the fissures and interferes with the function of the embedded particles. It is desirable therefore that the possibility of this compaction and deposition of debris in the fissures should be reduced or avoided.